In recent years, with increasing interests in maintenance and enhancement of health and prevention and treatment of diseases, many studies have been made on physiological functions of fish oil and of eicosapentaenoic acid (C20:5, EPA) and docosahexaenoic acid (C22:6, DHA), which are constituent components of the fish oil. Specifically, an anti-atherogenic action, a cerebral function improving action, a visual function improving action, an anti-tumor action, an anti-inflammatory action, and the like have been reported (Non Patent Document 1). In 2005, the Ministry of Health, Labour and Welfare defined a recommended total intake (adult) of DHA and EPA of 1 g/day, and use of a DHA and EPA-rich fat or oil has been desired.
On the other hand, a highly-unsaturated fatty acid-rich fat or oil has very low oxidative stability and is liable to produce deterioration odor and unpleasant odor/taste, and hence practical realization thereof is significantly restricted.
As technologies for improving oxidative stability of a fat or oil, there has been known, for example, a method involving adding a roasted sesame oil, an ascorbic acid ester, and an herb extract to a fat or oil containing a polyunsaturated fatty acid to stabilize the fat or oil (Patent Document 1). Further, there have been known a lipophilic antioxidant containing, for example, a bayberry extract and a rosemary extract (Patent Document 2), a lipophilic antioxidant containing gallic acid, a water-soluble antioxidant, and an oil-soluble antioxidant (Patent Document 3), and an antioxidant composition including an acetone extract of tea leaves together with a tocopherol and an ascorbic acid ester (Patent Document 4). In addition, the rosemary extract has been known to have high antioxidative property (Non Patent Document 2), an antioxidant including a rosemary extract that includes hexanal, carnosol, and carnosic acid in specified amounts (Patent Document 5), and the like have been reported.